On 06/19/2012 04:11 AM, gnehzuil.lzheng@xxxxxxxxx wrote:
> [CC'd to util-linux mailing list]
>
> On 06/18/2012 09:28 PM, Jens Axboe wrote:
>
>> On 06/18/2012 01:48 PM, Zheng Liu wrote:
>>> Hi Jens,
>>>
>>> I meet a problem when I use ionice(1) to adjust a process's io priority.
>>> I do the following operations:
>>>
>>> $ ionice -p${pid}
>>> none: prio 0
>>> $ ionice -p${pid} -c2 -n4
>>> $ ionice -p${pid}
>>> best-effort: prio 4
>>> $ ionice -p${pid} -c0 -n0
>>> $ ionice -p${pid}
>>> best-effort: prio 0
>>>
>>> So I cannot set scheduling class back to 'none'. If I call ioprio_set(2)
>>> directly, it will be fine. But if I use ionice(1), I cannot change it. I
>>> read the docs about ionice in [1]. I notice this code:
>>>
>>> switch (ioprio_class) {
>>> case IOPRIO_CLASS_NONE:
>>> ioprio_class = IOPRIO_CLASS_BE;
>>> ^^^^^^^^^^^^^^^^
>>> *It means that we cannot set back to none.*
>>> break;
>>> case IOPRIO_CLASS_RT:
>>> case IOPRIO_CLASS_BE:
>>> break;
>>> case IOPRIO_CLASS_IDLE:
>>> ioprio = 7;
>>> break;
>>> default:
>>> printf("bad prio class %d\n", ioprio_class);
>>> return 1;
>>> }
>>>
>>> My question is why we need to ban the user to set back to 'none'. Is there
>>> some reasons? Thank you.
>>
>> The kernel code does allow it, so it's only in the tool that this
>> restriction exists. I don't think we have a particularly good reason to
>> have it there. This is a tools question, though, not a kernel issue. I
>> suggest you take it up with the util-linux crew. I'm fine with removing
>> this restriction from ionice, especially since you could just roll your
>> own that did it.
>>
>
>
> Thanks for your reply. Hopefully we can get some feedbacks from
> util-linux crew.
That has already been fixed by commit v2.15-45-g5dc9371 more than 2 years ago:
Author: Jakob Unterwurzacher <jakobunt@xxxxxxxxx> 2009-01-17 02:38:32
Committer: Karel Zak <kzak@xxxxxxxxxx> 2009-05-27 23:43:18
and the change made it into 2.16.
The current piece of code looks like this:
switch (ioclass) {
case IOPRIO_CLASS_NONE:
if ((set & 1) && !tolerant)
warnx(_("ignoring given class data for none class"));
data = 0;
break;
case IOPRIO_CLASS_RT:
case IOPRIO_CLASS_BE:
break;
We'are currently at version 2.21.2.
Have a nice day,
Berny
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